Electrolytic method and apparatus for production of magnesium



u@ 6, w58 o. G. slvlLoTTl ET AL 3,396,094

ELECTROLYTIC METHOD AND APPARATUS FOR PRODUCTION OF MAGNESIUM Filed 00T.. 25, 1962 5 Sheets-Sheet 2 Aug, 1968 o.G.s|v|L.oTT1 ET Al- 3,396,094

ELECTROLYTIC METHOD AND APPARATUS FOR PRODUCTION OF MAGNESIUM Filed Oct. 25, 1962 5 Sheets-Sheet 5 RLECTROLYTIC METHOD AND APPARATUS PoR PRODUCTION 0F MAGNESIUM Filed Oct. 25, 1962 L A n H T O m w S G a 5 Sheets-Sheetl A 5 Sheets-Sheet 5 O. G. SIVILOTTI ETAL ELECTROLYTIC METHOD AND APPARATUS FOR PRODUCTION OF MAGNESIUMv 'Filed OCT.. 25, 1962 Aug.' 6, 1968 48 /m/emors O//vo 6. S/'v/Of/i Augusf/n Briand Eifel-CC s. AMMJLW Affomey Unit This invention relates to apparatus and procedure for electrolysis of molten baths and more particularly to the electrolytic production, from a fused bath, of a metal which as released in molten condition is lighter than the bath. In a specific and par-ticularly important sense, the invention is concerned with the production of magnesium by passage of current through a fused bath that contains magnesium in halide form.

A chief object of the invention is to provide improvement in the structure and operation of electrolytic cells such as shown and `described in U,S. Patent No. 2,785,- 121, granted March 12, 1957, on 'the application of Alan H. Johnston, for Electrolytic Apparatus.

In general, the cell structure of the patent comprises a main cell chamber and an adjacent collecting chamber, having their walls and bottom or oor constructed of massive refractory material, all within lan outer steel shell, the partition lbetween the chambers being a so-called curtain wall likewise of massive refractory construction, e.g. built up from the oor of the cell. lIn the main cell compartment there are a plurality of mutually spaced, parallel anodes suspended from the refractory-lined cover, each anode being a heavy graphite plate or the like which extends across the cell, i.e. perpendicular to the curtain wall and the opposite or back Wall of the chamber. Between successive anodes, and conveniently also at the outer ends of the array, are a plurality of metal cathodes, e.g. consisting of s-teel plates, mounted on supporting structure projecting through the rear wall of the chamber, the cathodes likewise extending perpendicularly to the curtain wall. The cathodes and the anodes are thus interspersed, i.e. in an interleaved, mutually spaced arrangement, with their forward edges adjacent the partition wall.

Inverted trough structures are provided above the cathodes for collecting the molten magnesium which rises on and from the cathodes, so as to guide it into the collecting chamber through appropriate openings in the curtain wall. These openings may consist of doorways extending to the floor of the cell, so that appropriate tools may be inserted through the fused bath in the collecting chamber to scrape or otherwise remove sludge from the bottom of the main compartment. The bath lls both chambers, to a level well above the openings in the curtain wall, so that Ithe latter structure effectively completes the enclosure of the main chamber, i.e. together with the cover for the latter.

In operation, current is passed from the anodes -to the cathodes, through the bath, to effect the desired electrolysis of the magnesium chloride in the bath. Gaseous chlorine released at the anodes collects in the enclosed space above the main chamber for appropriate withdrawal, while the molten magnes-ium deposited at the cathodes rises to the underside of `the inverted trough structures and is released into the collecting chamber, where it accumulates at the surface of the molten bath and is drawn off from time to time lto provide the desired product of metallic magnesium. In this way, the chlorine is isolated from the magnesium, while the entire cell structure is quite rugged and yet easily maintained, especially with respect to removal of sludge from the localities of the main chamber below the electrodes. Other advantages of d States Patent O 3,396,094 Patented Aug. 6, 1968 ice the apparatus are set forth in the above-mentioned patent and need not be repeated here.

While satisfactory operation has been obtained with cells constructed in this manner, the present invention is designed, as indicated above, to afford significant improvement in such cells and in their method of operation, for example with respect to a betterment of current efficiency and limproved yield or recovery, or both, of pure magnesium metal, as well as greater convenience in the collection and removal of metal, and in other respects.

A specic aim of the present improvements is to permit operation of the cell at substantially lower lbath temperatures than has heretofore been Ifeasible, it being now found -that if the molten bath can be kept at temperatures below about 690 C. and very preferably at or below 680 C., rather than at temperatures of the order of 710 C. to 720 C. or higher as previously employed, the operation is significantly improved, especially as measured by so-called current eiliciency. While the theory of this finding is not fully established, it is at present believed that an important aspect of the lower temperature is to improve the adhesion of molten magnesium to the steel plates which constitute the cathodes, apparently by increasing the viscosity of the electrolyte, so that near the cathodes the turbulence generated by the ascent of the chlorine bubbles at the anodes is reduced. Best operation appears t0 result when the deposited metal forms essentially a continuous layer, -in molten condition, on the cathode surfaces, so that it flows slowly upwards, following the plates and then the undersides of the troughs, for delivery in the front or collecting compartment without loss into the body of the bath (in the main chamber), it being understood that any metal escaping from the troughs or around them is consumed 'by reaction with chlorine yat the top of the bath.

In the ordinary operation of the described magnesium cells, the molten metal collects at the surface of the fused electrolyte in the side or supplemental compartment. It has been discovered that in order to keep the exposed, floating metal properly molten, i.e. to avoid freezing because of loss of heat by radiation from this metallic layer, the `bath temperature must generally be held at values well about 700 C., namely a point 50, or substantially more, above the usual melting point of magnesium (651 C.).

In accordance with the present invention the collecting chamber is provided with a special metal-collecting reservoir, eg. consisting essentially of a long inverted box of steel or the like, extending t-he length of the charnber above the openings in the curtain wall, the box or reservoir being positioned so that it is wholly submerged in the bath at all times. This reservoir is open orhas openings along its bottom into which the molten metal from the collecting troughs over the cathodes may rise. The metal thus gathers under the top of the box, being restrained and confined from floating further upward. At one end or at any other suitable locality there is an upwardly opening structure constituting a tapping well, which may serve both for removal of the produced metal and also, if desired, for insertion of additions to the bath. The top or upper plate of the collecting reservoir is conveniently arranged to slope gradually upwards toward this tapping well, so that the metal ows readily to the latter, from the localities where it is received.

Apart from certain further or subsidiary features of the above-described improvements in structure and procedure, these arrangements are of special advantage in a number of ways. In the rst place, the collected, molten magnesiurn rnetal is essentially Wholly maintained below the surface of the fused bath. In this fashion, the metal is kept effectively molten by the heat of the bath, without need for any supplemental heating means or the like. Hence the bath may be operated at the desired low ternperature. Relatively large quantities of metal may nevertheless be collected, so as to avoid any need for undue frequency of tapping.

A further, important feature is that by minimizing o-r indeed essentially wholly avoiding the exposure of the liquid metal to the atmosphere, burning and oxidation are correspondingly prevented. It has been found that magnesium oxide formed at the surface of the collecting chamber represents a deleterious contamination in the bath. If it reaches the cathodes, i.e. by dispersion through the molten salt mixture, it tends to be adsorbed by the molten magnesium there, with the effect of dispersing or breaking up the magnesium into small spheres or bodies. In turn the continuity of the ymagnesium layer or coating on the cathodes is broken and deposition tends to take place in localized spots or islands. When this effect occurs, it has been found that the current eiciency of the cell drops badly, e.g. to a value below 75%.

As explained above, it is believed that full current eiciency is largely dependent on maintainance both of a clean surface on the cathodes, and of a continuous coating on them of moderately viscous molten magnesium as the latter is deposited; thus the current flow extends unimpeded to all parts of the active cathode surfaces, while the collection and recovery of the metal is made as complete as possible. The avoidance of oxidation of the metal also, of course, directly improves the recovery of product in the operation, i.e. in that metal loss through such oxidation is correspondingly reduced. It will be understood that heretofore some effort has been made to decrease oxidation by coating the free metal surface with ux, but such expedient has not been very eifective in accomplishing the desired purpose.

As indicated, a primary function of the collection of metal in a bath-submerged reservoir in the side collecting chamber, is to permit lower bath temperatures, i.e. so as to provide a superior condition of the metal as it deposits on the cathodes (with advantages as noted above), and so as to avoid the necessity of increased specific power consumption for lthe sake of maintaining bath temperatures of the order of 720 C. and higher. As explained above, a temperature difference of the order of 40 or 50 between the bath and an exposed, oating metal layer ordinarily occurs because of heat radiation, in operation of the cell without the reservoir of the present invention. In contrast, it is found that with these irnprovements, the danger of metal freezing, in attempting -to operate at temperatures below 700 C., is wholly avoided, and the bath temperature can be safely and very advantageously dropped below 690 C., preferably below 680 C., and even to values approaching 660 C.

Certain embodiments of the invention, including certain further features of improvement, are described in detail hereinbelow, and are illustrated in the accompanying drawings, wherein:

FIG. l is a longitudinal vertical section of the complete cell, taken inside and along the front wall of the collecting chamber, showing the curtain wall and the improved reservoir and tapping well in elevation (but with the front of the reservoir partly cut away):

FIG. 2 is a fragmentary perspective view, with many parts broken away, of the cell structure, particularly with respect to the collecting chamber, taken as from the upper right-hand corner of FIG. l;

FIG. 3 is a transverse vertical section taken essentially on line 3-3 of FIG. l, but with certain upper parts and parts of one anode in elevation;

FIG. 4 is an enlarged transverse section of the tapping well, online 4-4 of FIG. 1;

FIG. 5 is an enlarged, fragmentary transverse section, similar to FIG. 4, on line 5--5 of FIG. l, showing the metal-collecting reservoir;

FIG. 6 is an enlarged, fragmentary, perspective view,

with parts broken away, of the tapping well and adja cent reservoir portion, seen as from the rear of FIG. 2;

FIG. 7 is a fragmentary, greatly enlarged view of a portion of the tapping well, seen as in FIG. 2, but wit-h ahbell cover for the tapping pipe in elevated or exploded view;

FIGS. 8 and 9 are respectively fragmentary, transverse sections, similar to FIG. 4, showing the situation of fused bath and collected metal respectively during periods of non-tapping operation, and during times when metal is to be removed;

FIG. 10 is a plan View of a modified form of reservoir and tapping well;

FIG. 11 is a longitudinal side elevation of the assembly of FIG. 10;

FIG. 12 is an enlarged transverse section on line 12--12 of FIG. l0, showing the tapping well;

FIG. 13 is Ian enlarged transverse section, taken as on line 13-13 of FIG. l0, showing the collecting reservoir and its relation to the curtain wall and the spouts of the inverted troughs over the cathodes;

FIG. 14 is a fragmentary, longitudinal vertical section of another modification of the reservoir and tapping well;

FIG. l5 is a transverse vertical section on line 15-15 of FIG. 14, but with 'fragments of certain details in elevation; and

FIG. l6 is a fragmentary, transverse vertical section showing a further modied form of tapping well for the collecting reservoir.

In the illustrated examples of the invention, the basic structure of the cell is essentially as shown in the abovecited Patent No. 2,785,121, to which reference may be had for such details and operational features as may not be shown or described herein.

Referring to FIGS. 1, 2 and 3, the apparatus is rectangular in shape and includes a main chamber 20 having a rear Wall 21 along its lon-ger dimension in plan, and end walls 22, 23, the front side of the chamber 20 being bounded by a partition or curtain Wall 24. Along the outer face of the partition wall a collecting or supplemental chamber 25 extends, being bounded at the ends by continuations of the walls 22, 23 and along its front side by a wall 26. All of t-he walls 21 to 26 inclusive, as well as the oor 27 under the entire cell, are made of heavy refractory construction, being conveniently built of refractory blocks (not shown as such) built up as masonry. The entire structure may have an outer insulating layer 29, and an outermost steel casing 30 for strength and protection.

The main chamber 20 has an outlet duct 32 near the top of one end wall 22, for withdrawal of chlorine gas, and is enclosed at t-he top by a removable, refractory lined cover 34, preferably seated in sealed relation over the chamber.

A plurality of heavy, plate-like graphite anodes 35 are mounted in the cover so as to project downward into the chamber 20 with their lower edges near the bottom of the latter and each in such position that its long dimension extends from front to rear of the compartment. Appropriate electrical connecting means 37 are provided at the upper ends of the anodes. The cell also includes a plurality of cathodes 40, which may consist of steel plates with laminating reinforcements, the cathodes being arranged at localities between successive anodes so that the electrodes alternate, in mutually parallel array along the main chamber 20, each extending substantially from the rear to the front walls of the chamber. For structural and operating convenience, the cathodes 40 that are disposed between pairs of anodes 35 are themselves arranged in spaced pair as shown in FIG. l, each such pair being carried by suitable mounting and electrical connecting structure 42 which extends through the rea-r wall 21 and has electrical connection means 43. The cathodes of each described pair are thus disposed suitably close to the respectively adjacent anodes 35. At the ends of the cell, single cathodes 40a are provided, each similarly supported and connected through the rear wall of the cell and arranged in suitable proximity to the adjacent anode 35.

To permit discharge of molten metal which deposits on the cathodes and flows upwardly, the curtain wall 24 has appropriate openings, which are conveniently in the form of doorways 45, i.e. opening from a level somewhat above the cathodes, all the way down to the floor of the cell so that sludge at the bottom of the main compartment may be raked or scraped through these doorways into the collecting chamber 25, and therefrom removed, -by suitable implements inserted through the chamber 25. If -desired or needed to help the ow of sludge towards chamber 25 during raking .and to promote collection of the sludge on the bottom of chamber 25 rather than of chamber 20 as soon as the sludge is formed during electrochamber 20 as soon as the sludge is formed during electrolysis and while it is still uid, the floor 27 of chamber 20 is inclined toward chamber 25.

For actual conveyance of molten ,magnesium into the compartment 25, inverted trough-like structures are lprovided over the cathodes, e.g. such as the inverted steel troughs 46 over each cathode (conveniently arranged in connected Vpairs over the central pairs of cathodes), having roof and guiding portions which extend through the openings 45 of the curtain wall and which slope upwardly from the rear wall 21 to an upturned spout portion 48 on each, inside the chamber 25. If -desired or needed for maximum collection of metal there may also lbe a plurality of auxiliary inverted troughs 50, each of monolithic refractory material, hollowed at its underside and disposed with its ends respectively seated in the rear wall 21 and curtain wall 24 of t-he main chamber. These auxiliary troughs, likewise sloping upwardly to the top of the openings 45, are dimensioned to overlie the central pairs of troughs 46 and also the end troughs 46 over cathodes 40a. Although .any magnesium which may deposit on the upper sides of the steel troughs 46 may well tend to adhere to the near-level surface of the latter and thus flow along it into the end compartment, the auxiliary troughs 50 may cooperate in collecting and guiding any such metal that may escape, into and through the doorways 45.

In operation, the chambers 20 and 25 of the cell are filled with fused bath to a level 52 well above the tops of the doorways 45, ie. near the top of the outer wall 26. It will be understood that such bath may be composed of a magnesium halide, together with other salts appropriate as a vehicle and for establishment of desired conditions of melting point, uidity and the like, all in accordance with well-known practice in the art of electrolytic production of magnesium from a molten electrolyte. More particularly, the magnesium salt is commonly magnesium chloride, the remaining constituents of the bath being other chlorides such as sodium and calcium chlorides, with perhaps a small amount of a fluoride, i.e. calcium fluoride. The magnesium chloride, which constitutes the source of the magnesium metal product, is usually maintained in minor proportion, the remaining salts serving to provide desired fluidity and conductivity. As an example, appropriate for operations described herein, including the use of the present invention, one satisfactory bath consists essentially of about 15% magnesium chloride, calcium chloride, 50% sodium chloride, together with a small amount of calcium uoride, i.e. 5% 0r less, all quantities being expressed by weight.

With a suitable source of direct current connected to the means 37, 43 so that electrical energy is supplied in the circuit and particularly in the path from the anodes 35 through the moltenbath to the cathodes 40, electrolysis proceeds, consuming the magnesium chloride in the bath and releasing chlorine at the anodes and metallic magnesium at the cathodes. The chlorine collects in gaseous form at the top of the main chamber 20, for discharge through the port 432, while the magnesium metal is deposited in molten state on the exposed cathode surfaces, flowing upward and collecting at the underside of the troughs 46. The magnesium metal is thus guided by the troughs and spouts 48, with the aid, if necessary, of the auxiliary troughs 50, into the collecting and charging chamber 25. In the apparatus of the above-mentioned patent, the molten product metal thus collects as a floating body at the top of the fused bath in the chamber 25, for removal from time to time. It will be understood that the bath is maintained in fused condition by the heat of electrolytic operation, i.e. the passage of current. Procedures for starting and operating the cell, as well as for adding charge of magnesium chloride from time to time, may be generally such as are known or understood in the ar-t, or as more fully explained in the patent.

In accordance with the present invention, an elongated reservoir or collecting box 55 is provided near the top of the collecting chamber 25, extending substantially the entire length of the chamber between `the end walls 22, 23. While other configurations or constructions, or other materials, may be employed in some cases, an especially convenient arrangement consists of a long, inverted sheet metal box, made of ordinary steel or the like, having a rear, vertical wall 56 which extends along, and preferably against the face of the curtain wall 24 above the doorways 45. The box has a Hat top or cover plate 57, having an appropriate, gradual slope, for example from the end wall 23 upwardly to a tapping box 60, which in the structure of FIGS. l to 9 terminates the metal collecting assembly at a locality immediately adjacent the end wall 22, but in some cases may be conveniently located near the center of the metal collecting reservoir, e.g. beside the central doorway. The metal construction of the reservoir 55, e.g. steel, affords a strong and leak-proof arrangement, and the top wall 57, being of metal, facilitates heat conduction from the bath to the molten magnesium and preservation of the latter in molten state.

The front wall 62 of the box 55 is spaced somewhat inward from the front wall 26 of the collecting chamber, and also slopes inward, at a considerable angle as shown, toward the bottom. This disposition, including the downward and inward slope, of the wall 62 is designed to permit ready insertion of appropriate rakes or other long implements that may be desired for collecting and extracting sludge from the bottom of the main chamber 20, below the cathodes, in the manner explained above. The underside of the box or reservoir 55 is open at least at regions adjacent the wall 24, but is preferably closed along its forward part, as by the bale or plate 63, which is shown as extending the length of the box and covering the bottom of the latter over about half (or more) of the area between the front wall `62 and the rear wall 56.

It will now be seen that the elongated, inverted box 55 is disposed so that the `spouts 48 of the metaladvancing troughs 46 open into the bottom of the box, i.e. through the elongated aperture, ample for such purpose, which lies between the baille 63 and the rear wall 56. The baille 63 serves to keep the contents of the box, especially the collected metal, relatively quiet despite any disturbance, surges or like movement of the fused bath, as for example when additions are made to the bath or sludge cleaning or other operations are effected in it. The entire structure of the reservoir 55 is disposed so that it lies wholly beneath the surface 52 of the bath, i.e. at least one inch or more below such surface at the highest end of the box (adjacent or in effect Within the tapping assembly a preferred arrangement being that the top 57 of the box be several inches, e.g. four to six inches, below the bath surface 52 at the tapping end, and several inches further below at the extreme or low end, adjacent the wall 23.

Although the tapping box 60' may in some cases constitute a simple well structure which communicates with the reservoir 55 and restricts the exposed, floating portion of the metal to the small area of the well, the

structure illustrated in FIGS. l to 4 and 6 to 9 embraces further features to exclude the metal from normal exposure while permitting ready access to it at desired times for tapping and while at the same time affording means for charging fresh electrolyte material into the cell. Thus the illustrated box 6G is an upright container of steel (in plate or sheet form) which projects to or above the normal bath level. As shown, it has spaced vertical side walls 65, 66, a front wall 67 which slopes downwardly from a position adjacent the top of the front wall 26 of the cell toward the curtain wall 24 (eg. in the same sloping plane as the reservoir wall 62), and a rear, vertical wall 68. All four of these walls terminate at the very top of the vessel, i.e. preferably above the bath level, while the side walls 65, 66 and the front wall 67 extend to a bottom plate 69 at a region substantially below the level of the bottom batile 63 of the collecting reservoir, so as to provide a lower extension 70 of the well, which is closed by the bottom plate but has a side opening 71 in the wall 66.

The rear wall 68 of the main part of the tapping box is .ush with, and may be a continuation of, the rear wall 56 of the reservoir, while the lower extension 70 of the tapping well is completed with a vertical rear wall 72 spaced forward from the wall 68 and from the refractory cell partition or curtain wall 24. The wall 72 conveniently extends upward to the level of the top 57 of the reservoir, so that metal from the reservoir will tend to ow into the space between this wall and that of the wall 68 which constitutes a continuation of the reservoir rear wall 56. A shelf 74 extends horizontally across the interior of the tapping box 60 at the level of the top 57 of the reservoir, so as to cover the space between the walls 72 and 68. This covered space, into which metal from the reservoir tends to ow, thus in effect constitutes a continuation of the reservoir, and indeed may directly receive metal from the trough over the outermost end cathode a next to the cell wall 22.

The tapping assembly 6() thus provides a deep well extending from the top of the box down into the lower extension 70 (which opens sidewise near the bottom), and an isolated compartment at the rear of the wall 72, which is defined by the shelf 74 and the lower part of the wall 68, and which normally segregates the molten metal from the liquid bath that substantially fills the main body of the well. Means are provided whereby molten metal from the reservoir can be withdrawn through the tapping well. Although other structures may be employed for intermittently allowing metal to ow into the main part of the well, the drawings show a convenient arrangement whereby an air lock is employed to block the flow of metal except at times when tapping is to be performed.

For such purpose, the shelf 74, covering the end exextension of the reservoir, has an upstanding tube or pipe 75, opening through the shelf and khaving its open top at some distance below the normal surface of the electrolyte bath. This opstanding pipe receives a removable bell or cover 76, consisting of an inverted cup having a depending skirt :portion 77 which very loosely surrounds the pipe 75, a top handle 78, and an internal pin or rod 79, extending diametrically across the cylindrical skirt 77 and .adapted to rest on the upper edge of the pipe section 75. Thus the bell seats loosely over the pipe, as shown in FIGS. 4, 8 and 9, with the pin 79 resting on the upper end of the pipe and with abundant clearance between the pipe and bell at all localities, as well as between the lower edge of the bell and the shelf 74.

In normal operation the bell 76 is so seated on the pipe 75 as to entrap a substantial pocket of air 80 under the bell, i.e. as seen in FIG. 8. This may be accomplished, when the apparatus is full of molten electrolyte, simply by pushing the bell straight down into the bath until it rests on the pipe, so that air is caught under it. The resulting `air pocket prevents communication between the interior of the collecting box or reservoir and the main part of the tapping well 60. As seen in FIG. 8, the seated bell 76 is then entirely below the surface 52 of the molten electrolyte 82, which rises only to a level 83 in the space between the skirt 77 and the pipe 75, below the top of the latter. Molten metal 84, which has collected in the reservoir and its extension -between the walls 68 and 72, rises in the pipe 75, but is likewise prevented by the air pocket from going above the level 85, which is also below the top of the pipe. Hence the air cushion or lock 80, under the bell, effectively functions as a valve to keep the metal from owing upward into the main portion of the tapping well.

At times when there is enough accumulation of molten metal in the reservoir to be tapped, the bell 76 is removed, releasing the air and thus allowing the metal to ow up through the pipe 75 to the surface of the bath in the main part of the well. If desired, as for regulating the rate of metal ow or at least for avoiding-inadvertent loss of the bell, the latter may be replaced in such a way as not to entrap any air, for example by inserting it in the well in a sidewise or inverted position, and then, beneath the level of molten material, turning it and seating it over the pipe 75. In such circumstances, the situation is as depicted in FIG. 9, where the molten metal 84 now lls the upper part of the tapping well, flowing into the latter from the reservoir through the pipe 75 and around under the bell 76. The molten magnesium metal is tapped from the well through suitable means such as the pipe 88, operating by siphon or appropriate pumping action. When sufficient metal has been removed, the bell '76 may be withdrawn and replaced directly downward so as to reestablish the air pocket 80. The liquid metal remaining in the outer part of the tapping well 6l) is then withdrawn, and the situation of FIG. 8 is restored, i.e. for continuing operation of the cell until tapping is to be repeated.

As shown in FIGS. 2, 3, 4 and 5, the partition wall 24 of the cell has a narrow shelf or ange which projects into the supplemental compartment all the way along the wall, so that the rear wall 56 of the collecting box is disposed above this shelf, i.e. conveniently resting upon it. In this fashion escape of metal between the steel wall 56 of the reservoir and the face of the refractory wall 24 is avoided, experience having indicated that seepage of metal is apt to occur through unsealed or unguarded cracks or openings, Ihowever small.

For charging bath ymaterial into the cell, e.g. additional magnesium chloride usually preheated to a molten state, the main portion of the tapping well can be used. With the metal reservoir sealed off by the air gap under the bell 76, additional bath ingredients are simply poured into the exposed region of bath in the tapping well 60, causing movement of such material into the main .part of the bath through the side port 71 of the lower extension 72. The somewhat tortuous course thus provided for the entering charge material serves to avoid sur-ges or other vigorous rdisturbances in the molten bath, so that unwanted disturbance of the collected metal in the reservoir is prevented, and there is no excessive dislodgment and disper sion of sludge or contaminating particles that may have settled to the bottom of the cell.

The side wall 66 of the tapping well also has a small opening 92 (FIGS. 3, 4 and 6) at approximately the level of the bottom baille 63 of the reservoir, and disposed adjacent the front wall 67 of the well. At this locality the baffle 63 is advantageously constructed to include a short upwardly sloping section 94, which connects the baffle with the wall 66 at a locality just above the opening 92, i.e. so that the latter opening communicates with the `bath immediately below this shield section 94, but is partly guarded at its forward end by the adjacent part of the box wall 62. With this arrangement, any metal that might overflow the collecting reservoir will tend to run under the shield 94 and enter the tapping well through the opening 92, it being understood that although normally the cell is tapped so that the molten metal is kept well above the bottom of the reservoir 55, it is possible that because of inadvertent overfilling or because of violent bath disturbance, the reservoir may overfiow, so to speak, in a downward direction. Such overfiowing metal tends to fiow along the underside of the reservoir, and thence into the well through the port 92, rather than into the larger body of `bath outside.

The reservoir and tapping well can be supported in any suitable manner, for example as by :brackets or flanges extending over the top edges of the refractory cell walls. As examples of such structure, a bracket 95 is shown at the end of the box in FIG. 1, resting on the wall 23, while flange structure 96 (FIG. 2) is shown as part of the tapping Well, at the other end of the collecting compartment.

Cover means may also be provided for the collecting compartment 25 or parts of it such as the tapping well. One effective structure is constituted by a refractory lined, steel jacketed cover 98, hinged about a horizontal axis along the face of the cell wall 24, i.e. at 99, and arranged to be closed down in covering relation to the entire side chamber 25 of the cell. It has been found that such a structure not only reduces oxidation and other contamination of the bath, and effectively conserves heat, but also provides a convenient means of adjusting the cell temperature. Thus if t'he bath is found to have a temperature above a range or value regarded as optimum for cell operation, e.g. 680 C., the cover is raised until the cooling action of the air on the exposed bath surface 52 brings the temperature to the stated, desired value.

It will now be seen that the described arrangements, providing an enclosed, submenged reservoir for collection of the molten metal product, effectively fulfill the stated objects of the invention. In operation of the cell, with current fiowing between anodes and cathodes, magnesium is deposited in molten form at the cathodes, rising to the inverted troughs 46 and running forward, via the spouts 48, so as to discharge upwardly within the reservoir 55, including the extended portion thereof behind the wall 72 of the tapping well. The metal collects as a layer directly against and under the top 57 of the reservoir, 'becoming deeper as `more metal is produced.

The molten bath is at all times maintained at a level well above the reservoir (within the refractory cell walls, which extend substantially above the top of the reservoir), so that there is neither exposure of the metal to the air, nor exposure of any substantial extent of metal structure which is in contact `with the metal. Stated in another way, the invention avoids the relatively large temperature gradient that occurs between the top and bottom of the molten metal when it is exposed above the bath across the collecting chamber, and thus with the invention there is no need for a relatively high bath temperature to overcome such gradient and keep the metal surface from freezing. In consequence the cell is operated at a substantially lower temperature than might otherwise be possible, and corresponding improvement in efiiciency is achieved.

All tapping is accomplished through the tapping well 60 where by virtue of the preferred arrangements, molten metal is preferably excluded at all times except when tapping is actually in progress. On such occasions, simple manipulation of the bell 76 permits metal to rise in the well for desired withdrawal.

Charge of the cell is effectively achieved through the same tapping well 60, preferably without substantial disturbance of the bath. By virtue of the spaced relation of the collecting box and its shape, the chamber 25 also serves its further function of permitting access to clean the cell, as by insertion of appropriate implements, between the front wall 26 and the box 55, for scraping and pulling out sludge from the bottom of the main chamber 20.

The following is an example of the process of producing magnesium by electrolysis with the operation of keeping the molten metal in a confined region below the bath surface as it is collected in the side compartment of a cell having the described basic ar-rangement for effective achievement of a large production rate: The fused bath was provided having a composition as specifically indicated above, and at all times its surface 52 was kept well above the collecting box 55. The temperature of the bath, being essentially uniform throughout the main and supplemental chambers of the cell, was maintained in the range of 670 C. to 680 C., control being exercised when necessary by adjustment of the refractory cover 98 over the side compartment 25, i.e. closing the cover when the bath tended to become too cool, and raising it when the temperature rose to 680 C. or higher. Feed of electrolyte material, essentially consisting of molten magnesium chloride, was effected through the tapping well 60 at regular intervals, e.g. three times in each twenty-four hour day, and tapping of molten magnesium was effected at similar intervals, conveniently shortly after each feeding.

It was found that effective results were obtained by removing sludge from the bottom of the cell not more than about once a week, thus minimizing the temporary adverse effect of this disturbance which tends to disperse magnesium oxide and other impurities in the bath. Other conditions and features of operation, including the regulation of the bath composition, were essentially as are conventional for the electrolytic production of magnesium from magnesium chloride in a fused bath, except that daily additions of calcium fluoride (fiuorspar) were preferably (although not necessarily) higher than usual, c g. 20 to 60 pounds, instead of 15 pounds, per day. It will be understood that the uorspar functions to promote clarity of the bath and to cooperate in cleaning the cathodes, particularly when the bath has been disturbed as in making additions 0f feed or in removing sludge. Another important function of the fluorspar additions is to promote the formation of a thin frozen crust on the exposed surface of the bath in chambe-r 25, thus reducing rapid evaporation of bath constituents and, more important, preventing contact and consequent reaction of magnesium chloride with moisture of the air. Although for admixture to achieve the internal effects fluorspar can be added before cell feeding, crust formation is achieved by spreading the fluorspar in a thin layer on the bath surface, e.g. by dispensing 3 to 5 lbs. of it through a 28 mesh screen, and leaving it there without stirring. Results have been best when the tiuorspar particles are added in such amount and manner that none remain unwetted by the electrolyte and the crust formed is continuous.

Throughout the operation it was observed that the cathode walls were clean and that the magnesium adhered t0 them well in a continuous layer, owing slowly upwards in the desired fashion. The maintenance of the bath at 680 C. or below contributed greatly, it is believed, to the proper deposition and adhesion of the magnesium, i.e. by increasing its viscous properties and otherwise, as has been explained. The results of operation in this manner were highly satisfactory, and current efiicienies of to were regularly obtained, such etiiciency being a measure of the yield of magnesium relative to the yield theoretically obtainable by the current passed through the cell.

Although for most practical work it is desirable to keep the bath above 670 C. and preferably at 675 C., in some cases it is possible to operate (for perhaps very highest efficiency) at temperatures as low as 660 C. Such temperatures, however, have some disadvantage, in that there is increased danger of.rather prompt freezing of the magnesium during shutdowns.

FIGS. 10 to 13 inclusive illustrate a modified form of the collecting reservoir, which can be mounted in the side chamber 25 of the cell shown in FIGS. l to 3 inclusive, in similar fashion to the box 55. In the arrangement of FIGS. 10 to 13, the collecting box 102 consists of an inverted metal box running essentially the entire length of the side cell compartment and disposed adjacent the refractory wall 24, but in this instance actually constructed in two sections 102er, 102b, with a tapping well 104 between them. The forward part of the bottom of the box structure 102 is partly closed, as by the baille 105 (FIG. 13), but leaving a suicient horizontal opening, all the way along the compartment, so that guide portions .106 of the metal collecting troughs 46 may direct molten magnesium into the box. The tapping well 104 is here shown as simplyan open-topped box into which the reservoir sections 102a, 102b respectively communicate through side openings as indicated at 108 in FIG. 12. The upper or top walls ln, 110b of the box sections 102a, 102b slope gradually upwardly toward the central tapping well 104, to facilitate movement of molten metal toward the well. As in the case of the reservoir 55, the arrangement is supported so that the box sections 102a, 102b, made of steel, are wholly submerged beneath the surface of the molten electrolyte bath. The assembly is supported in appropriate manner, as by the brackets 112, 113 at opposite ends of the structure, resting on the side compartment walls 22, 23 with further support as needed, such as the central bracket 114.

Although if desired the tapping well 104 of the device just described may include further means for isolating the metal from the external atmosphere except at desired times of tapping, the arrangement is simply shown as an open well into which molten metal normally communicates, but is confined to at least a small area of continuous exposure. In general the function of the reservoir in FIGS. 10 to 13 is similar to that of FIGS. 1 to 3, although the arrangement of FIGS. l to 3 has certain special features and advantages, as has been explained.

In FIGS. 14 and l5 the collecting box 120 is constructed and disposed in generally similar manner to the corresponding parts of earlier numbered figures, so that molten magnesium 121 collects underneath the top wall 122 of the box. The feeding and tapping means are here located centrally of the reservoir, and include a separate feeding well 124 which simply provides a passage through the box without communication to the interior thereof.

The tapping well 125 opens above the level 126 of the molten electrolyte and extends to the bottom wall 128 of the reservoir. It has no direct communication with the latter but opens at the bottom of one side 129 into a shallow box 130, i.e. in the form of a shallow enclosure above the bottom wall 128. This box 130 is closed from the interior of the reservoir 120, except through an upright pipe 131 extending from the top of the box 130 to' a locality close to the underside of the upper reservoir wall 122.

The arrangement of the pipe 131 and box 130 with the tapping well 125 provides an effective hydrostatic trap, for isolation of molten metal, or appreciable quantities of it, from the atmosphere. At the .outset of operations, the well 125 is lled with molten salt electrolyte, as are all other parts of the cell. Molten magnesium 121 collects under the upper wall 122 of the reservoir 120, but the well 125, the box 130 and the major part of the pipe 131 that constitutes a vertical leg of the trap being filled with electrolyte, there is no Way for the magnesium to reach the well. After a sufficient accumulation of metal 121 to warrant tapping, removal of liquid from the well 125, as by dipping or by Siphon, causes flow downward through the pipe 131, bringing molten metal correspondingly down below the top of the box 130, so that it rises to the top of the liquid in the well 125. Further removal of metal effects continuance of the ow through the trap from the accumulated molten body 121, until tapping is completed, for example, at the point where molten bath begins to enter the pipe.

FIGS. 14 and 15 also illustrate supplemental means, useful in some cases, for promoting circulation of the electrolyte and for relieving undue surges or disturbances at times of feeding or the like. Thus vertical pipes, such as indicated by the pipe 133, may extend through the collecting box at a number of localities to afford better communication of electrolyte at full temperature between the main body of the bath and the portion above the box. Similarly FIG. 15 illustrates a window 135 in the front wall 24a of the main chamber, i.e. the partitioning wall, such window being disposed above the doorway 45a, the latter corresponding to the doorways 45 in the structure of FIGS. l, 2 and 3. It will be understood that a plurality of such windows may be provided, respectively above the doorways in the curtain wall, for improved communication of electrolyte between the main and collecting chambers, the windows being located below the electrolyte level 126 so that full isolation of the chlorine-containing space at the top of the main chamber is maintained.

In FIG. 16 a still further arrangement of metal tapping box is shown, it being understood that the illustrated device is located at a central or end position of the collecting reservoir, not shown in this view except in section at 140. The tapping well itself simply constitutes an upward column 141 opening into the top of the box 140 and having inwardly and upwardly tapering walls. A refractoryinsulated cover 142, of the nature of a bell, seats over this well 141, being sealed by the molten electrolyte 143 which rises to its level 144 around the bell, the latter being removable, as for manual tapping of molten metal.

FIG. 16 also illustrates an arrangement of a tap hole 146 in the front wall 26a of the supplemental chamber, such hole communicating via a trap or U-shaped conduit 147 `with the interior of the well 141. Advantageously, a tube 148 is arranged to deliver suitable gas under pressure, such as nitrogen, into the space beneath the bell 142, the pressure depressing the level of molten metal 149 below the upward opening 150 of the discharge pipe 147. The nitrogen simply bubbles out under the skirt of the bell, through the bath, while maintaining desired leveldepressing pressure. Although not essential, a similar pressure of nitrogen may be kept at the head of the other leg of the U-pipe 147, as by means of a tube 152 through a plug 153 in the tap hole 146. When it is desired to withdraw molten magnesium from the device of FIG. 16, the plug 153 is removed and supply of gas reduced or interrupted through the pipe 148. The metal 149 then rises in the well 141, and flows out through the pipe 147 and the tap hole 146, e.g. until all desired metal has been withdrawn from beneath the elongated top wall (not shown) of the collecting reservoir.

It is to be understood that the invention is not limited to the specific structures herein shown and described, but may be carried out in other ways without departure from its spirit.

We claim:

1. In a process for production of magnesium by electrolysis of magnesium chloride in a fused bath, wherein the bath is maintained, in molten form, in a main cell chamber and an adjacent supplemental chamber separated from the main chamber by a partition wall, said electrolysis effecting .deposit of molten magnesium on metal cathodes submerged, along with anodes, in the main chamber, and wherein molten magnesium is received above the cathodes within the main chamber and guided through the partition wall beneath the surface of the fused bath into the supplemental chamber for collection there, the improvement which comprises the steps of maintaining the fused bath at a temperature above the melting point ,of magnesium and below 700 C., and keeping the collected magnesium molten in the supplemental chamber by receiving and collecting the molten magnesium, which is directed through the partition wall, in an upwardly enclosed region that extends along said supplemental chamber within the latter and that is maintained submerged beneath the surface of the fused bath, and withdrawing molten magnesium as product, from a locality of said enclosed region.

2. A process as defined in claim 1, wherein the step of maintaining the fused bath at a temperature defined as aforesaid, consists in maintaining the fused bath at a temperature between about 665 C. and about 685 C.

3. A process as defined in claim 2, wherein the fused bath temperature is kept in the range of 670 C. to 680 C.

4. A process as4 defined in claim 1, wherein the fused bath in the supplemental chamber is kept with its surface substantially exposed across and along said chamber, and wherein maintenance of the aforesaid temperature of the bath is effected by controlling the application of air over the supplemental chamber to regulate the rate of heat loss from said exposed surface.

5. A process as defined in claim 1, in which the fused bath in the supplemental chamber is kept with its surface substantially exposed across and -along said chamber, and which includes intermittently supplying finely divided solid calcium fluoride to the supplemental chamber for providing a layer of said fluoride over said su-rface of the fused bath to promote maintenance of a frozen crust lat said surface.

6. In a process for production of magnesium by electrolysis of magnesium chloride in a fused bath, wherein the bath is maintained, in molten form, in a main cell chamber and an adjacent supplemental chamber separated from the main chamber by a partition Wall, said electrolysis effecting deposit of molten magnesium on metal cathodes submerged, along with anodes, in the main chamber, and wherein molten magnesium is received Iabove the cathodes within the main chamber and guided through the partition wall beneath the surface of the fused bath into the supplemental chamber for collection there, the improvement which comprises the steps of maintaining the fused bath at a temperature above the melting point of magnesium and `below 700 C., and keeping the collected magnesium molten in the supplemental chamber and inhibiting oxidation of said magnesium, by receiving and collecting the molten magnesium, which is dilrected through the partition wall, in an upwardly enclosed region that extends along said supplemental chamber within the latter and that is submerged beneath the surface of the fused bath, and withdrawing molten magnesium from time to time `at a tapping region, in said supplemental chamber, which communicates with the enclosed region and which provides not more than a small area of metal exposure relative to the metal-collecting -area of the enclosed region.

7. A process as defined in claim 6, wherein the step of maintaining the fused bath at -a temperature defined `as aforesaid, consists in maintaining the fused bath at a temperature between about 670 C. and about 690 C., wherein the fused bath in the supplemental chamber is kept with its surface substantially exposed across and along said cham-ber, and wherein maintenance of the aforesaid ltemperature of the 'bath is effected by controlling the application of air over the supplemental chamber to regulate the rate of heat loss from said exposed surface.

8. In a process for production of magnesium by electrolysis of magnesium chloride in a fused bath, wherein the bath `is maintained, in molten form, in a main cell chamber and an adjacent supplemental chamber separated from the main chamber by a partition wall, said electrolysis effecting deposit of molten magnesium on met-al cathodes submerged, along with anodes, in the main chamber, and wherein molten magnesium is received above the cathodes within the main chamber and guided through the partition wall beneath the surface of the fused ybath into the supplemental chamber for collection there, the improvement which comprises the steps of maintaining the fused bath -at a temperatu-re between about I665 C. and 685 C., by regulating heat loss from the bath, and keeping the collected magnesium molten in the supplemental chamber 'by receiving and collecting the molten magnesium, which is directed through the partition wall, in an upwardly enclosed region that extends along said supplemental chamber within the l-atter and that is maintained submerged beneath the surface of the fused bath, and withdrawing molten magnesium as product, from a locality of said enclosed Iregion, while exposing molten magnesium to the space above the supplemental chamber, at said locality, only over an area which is small relative to the metal-collecting area of the enclosed region.

9. In a process for production of magnesium by electrolysis of magnesium chloride in a fused bath, wherein the bath is maintained, in molten form, in a main cell chamber and an adjacent supplemental chamber separated from the main chamber by a partition Wall, said electrolysis effecting deposit of molten magnesium on metal cathodes submerged, along with anodes, in the main chamber, Iand wherein molten magnesium is received above the cathodes Within the main chamber and guided through the partition wall beneath the surface of the fused bath into the supplemental chamber for collection there, the improvement which comprises the steps of maintaining the fused bath at a temperature above the melting point of magnesium and not higher than about 690 C., and keeping the collected magnesium molten in the lsupplemental chamber by receiving land collecting the molten magnesium, which is directed through the partition wall, in an enclosed region that is upwardly closed by a metal sheet cover and that extends along said supplemental chamber within the latter and that is maintained submerged lbeneath the surface of the fused bath, said fused bath being maintained over and in direct contact with the entire upper face of said cover, and said collected molten magnesium being maintained in direct contact with the under face of said cover, and withdrawing molten magnesium as product, from a locality of said enclosed region.

10. In apparatus for electrolysis of a fused bath to produce at the cathode a metal lighter than the bath, which apparatus comprises wall structure defining a main cell chamber and a supplemental chamber both arranged to hold fused bath, said Wall structure including a refractory partition wall spearating said chambers and apertured to provide free communication of fused bath between the chambers, an array of cathodes and anode means in said main chamber, and means above the cathodes for receiving and conducting molten metal through the partition Wall, at a plurality of localities along the latter, into the supplemental chamber: the combination therewith of box means in the supplemental chamber for collecting molten metal, having a closed top and open at a lower part for communication with the fused bath, said box means extending lengthwise of the partition wall and being disposed to receive molten metal from the means above the cathodes so that said metal collects under the closed top of the box, said box means being arranged to provide free communication of fused bath vertically past it so that it can be covered by fused bath, and said box means having associated metal-receiving means to provide for removal of molten metal which has collected in the box means, and said wall structure, including said partition wall, being arranged to hold fused bath in both chambers to a level above the cathodes, the means above the cathodes, the apertured regions of the partition wall and the closed top of the box means, so that the chambers are wholly separated by said partition wall at regions above the fused bath, and so that said box means is maintained substantially submerged in the fused bath with its closed top covered by said bath in order to keep the collected metal molten.

11. Apparatus as defined in claim 10, wherein the box means is made of metal and is disposed in abutment with the partition wall, the means for conducting molten metal into the supplemental chamber comprises guide means extending from the locality of the cathodes through the partition wall to localities beneath the box means, and

wherein the box means includes a vertical wall atwise abutting the partition wall and having a horizontal lower edge, and wherein the apparatus includes a flange projecting from the partition wall into the supplemental chamber below said lower edge and above said guide means, to keep molten metal from rising between said box wall and said partition wall.

12. In apparatus for electrolysis of a fused bath to produce at the cathode a metal lighter than the bath, which apparatus comprises wall structure defining a main cell chamber and a supplemental chamber both arranged to hold fused bath, said wall structure including a refractory partition wall separating said chambers and apertured to provide free communication of fused bath between the chambers, an array of cathodes and anode means in said main chamber, and means above the cathodes for receiving and conducting molten metal through the partition wall, at a plurality of localities along the latter, into the supplemental chamber: the combination therewith of box means in the supplemental chamber for collecting molten metal, having a closed top and open at a lower part for communication with the fused bath, said box means extending lengthwise of the partition wall and being disposed to receive molten metal from the means above the cathodes so that said metal collects under the closed top of the box, said box means being arranged to provide access to the fused bath in the supplemental chamber for the introduction of material to the bath, and said box means having associated metal-receiving means in the supplemental chamber, communicating with the box means and opening to a region outside the aforesaid chambers, to provide for removal of molten metal which has collected in the box means, and said wall structure, including said partition wall, being arranged to hold fused bath in both chambers to a level above the cathodes, the means above the cathodes, the apertured regions of the partition wall and the closed top of the box means, so that the chambers are wholly separated by said partition wall at regions above the fused bath, and so that said box means is maintained substantially submerged in the fused bath with its closed top covered by said bath in order to keep the collected metal molten.

13. Apparatus as defined in claim 12, wherein apertured regions of the partition wall extend to the bottom of the main cell chamber and are shaped to provide mechanical access, through the supplemental chamber and the fused bath therein, to the bottom of the apparatus for removal of sludge from the main cell chamber, the box means in the supplemental chamber being shaped and disposed to permit said mechanical access, and the bottom of the main chamber being sloped downwardly and forwardly toward the bottom of the supplemental chamber to promote the forward flow of sludge in the main chamber and facilitate the removal of sludge therefrom.

14. Apparatus as defined in claim 12, wherein the metal-receiving means comprises well structure communicating with the box means and opening upwardly in the supplemental chamber through the main body of fused bath therein.

15. Apparatus as defined in claim 14, which includes trap means providing the communication between the well structure and extending between a lower part of said well structure and an upper interior region of the box means, to prevent flow of collected molten metal from the box means into the well structure until liquid is removed from the well structure.

16. Apparatus as delined in claim 12, wherein the metal-receiving means includes conduit structure communicating with the box means and extending through an adjacent outer part of the wall structure which delines the supplemental chamber, for withdrawal of molten metal through said conduit structure at desired times.

17. Apparatus as defined in claim 12, wherein the partition wall has lower apertured regions through which the molten metal receiving and conducting means conducts molten metal for collection in the box means and through which access is obtainable for removal of sludge from the main cel] chamber, and upper apertured regions adjacent the box means for promoting circulation of fused bath between the main and supplemental chambers.

18. Apparatus as dened in claim 12, wherein the box means includes conduit means vertically traversing the same at an intermediate region thereof, closed from the interior of the box means but opening both below and above the box means for promoting communication of fused bath between regions below and above the box means.

19. In apparatus for electrolysis of a fused bath to produce at the cathode a metal lighter than the bath, which apparatus comprises wall structure defining a main cell chamber and a supplemental chamber, including a refractory partition wall separating said chambers, a plurality of cathodes and a plurality of anodes in said main chamber extending crosswise thereof at an angle to said partition wall, said anodes and cathodes being disposed in alternating, parallel array, and means above the cathodes for receiving and conducting molten metal through the partition wall into the supplemental chamber, said partition wall being apertured for free communication between the chambers so that the fused bath occupies both chambers, and said supplemental chamber being substantially coextensive with the main chamber, lengthwise of the partition wall: the combination therewith of a collecting box for metal, mounted in said supplemental chamber adjacent said partition wall and extending substantially the length of said wall, said box being closed at its top and open substantially along its bottom, means for guiding molten metal from all of the aforesaid receiving and conducting means into said box, said box being disposed above said receiving and conducting means, said box being spaced from outer wall structure of the collecting chamber to provide access through the fused bath to the oor of the main chamber, and said box having associated metal-receiving means communicating with the box and accessible exteriorly of the bath in said supplemental chamber, to provide for tapping of molten metal, said chamber-defining structure, including said partitioning wall, being arranged to hold fused bath in both chambers to a level wholly above said collecting box as well as above said metal-receiving means in order to keep the collected metal molten, as well as above said cathodes and apertured regions of the partitioning wall, and said partitioning wall wholly separating said chambers at all localities above the fused bath.

20. In apparatus for electrolysis of a fused bath to produce at the cathode a metal lighter than the bath, which apparatus comprises wall structure dening a main cell chamber and an adjacent, coextensive supplemental chamber both arranged to hold fused bath, said wall structure including a refractory partition wall separating said chambers and apertured to provide free communication of fused bath between the chambers, an array of cathodes and anode means in said main chamber, and means above the cathodes for receiving and conducting molten metal through the apertured regions of the partition wall, at a plurality of localities along said partition wall, into the supplemental chamber: the combination therewith of box means in the supplemental chamber for collecting molten metal, having a closed, metallic top and open at a lower part for communication with the fused bath, said box means extending substantially throughout the length of the supplemental chamber and being disposed to receive molten metal from the means above the cathodes so that said metal collects under and against the closed metallic top of the box, said box means being arranged to provide access to the fused bath in the supplemental chamber for the supplying of replenishing material to the bath, and said box means having an associated metal-receiving well in the supplemental chamber, communicating with the box means and opening upwardly in the supplemental chamber for access from above the fused bath, to provide for removal of molten metal which has collected in the box means, and said wall structure, including said partition wall, being arranged to hold fused bath in both chambers to a level above the cathodes, the means above the cathodes, the apertured regions of the partition wall and the closed top of the box means, so that the chambers are wholly separated by said partition wall at regions above the fused bath, and so that said box means is maintained substantially submerged in the fused bath with its closed, metallic top covered, in direct contact, by said bath in order to keep the collected metal molten.

21. Apparatus as dened in claim 20, wherein the apertured regions of the partitioning wall extend to lower parts of the latter and are shaped to provide mechanical access, through the supplemental chamber and the fused bath therein, to the bottom of the main chamber for removal of sludge therefrom, and wherein said supplemental chamber has a front wall which is opposite and parallel to the partition wall, said box means being spaced substantially from said front wall and having a metal retaining wall along its side nearer to said front wall, which is sloped downwardly and inwardly toward the partition wall, said spaced arrangement and said sloped wall of the box means being constructed and arranged to afford mechanical access from the top of the supplemental chamber through the fused bath to the aforesaid apertured regions of the partition wall, for the aforesaid removal of sludge from the main chamber.

22. Apparatus as dened in claim 20, wherein the metal-receiving well comprises a vessel extending vertically both above and below the box means, and opening into the supplemental chamber so that said well communicates with the fused bath and provides the arrangement for supplying of replenishing material to the bath, passage means communicating between the box means and the vessel, and movable closure means for said passage means, to prevent travel of molten metal into the vessel except at desired times for tapping, so that the vessel is filled with fused bath at other times.

23. Apparatus as defined in claim 22, wherein the passage means comprises a pipe extending from the box means and opening upwardly in the vessel below the surface of the fused bath, and the movable closure means comprises a bell which is seated over the pipe selectively in a manner to entrap and not to entrap a volume of air for correspondingly blocking and permitting travel of molten metal into the vessel.

References Cited UNITED STATES PATENTS 1,833,425 11/1931 Jessup 204-70 1,851,817 3/1932 Dow 204-245 2,882,434 8/ 1945 McNitt.

2,785,121 3/1957 Johnston 204-247 2,888,389 5/1959 Williams et al. 204-70 ALLEN B. CURTIS, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,396,094 August 6, 1968 Olivo G. Sivilotti et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 22, "maintainance" should read` maintenance Column 4, line 70, "pair' first occurrence, shouldzread pairs Column 5, line l6, cancel "chamber 20. as soon as the sludge is formed during electro". Column 7, line 30, "of the wall 68" should read part of the wall 68l Column l0, line 59, "efficienes should read efficiencies Column ll, line l5, "upwardly" should read Colurrm' 18, line 26, 2,882,434 should'read 2,382 ,434

Signed andsealedthis l0th"day"of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

1. IN A PROCESS FOR PRODUCTION OF MAGNESIUM BY ELECTROLYSIS OF MAGNESIUM CHLORIDE IN A FUSED BATH, WHEREIN THE BATH IS MAINTAINED, IN MOLTEN FORM, IN A MAIN CELL CHAMBER AND AN ADJACENT SUPPLEMENTAL CHAMBER SEPARATED FROM THE MAIN CHAMBER BY A PARATION WALL, SAID ELECTROLYSIS EFFECTING DEPOSIT OF MOLTEN MAGNESIUM ON METAL CATHODES SUBMERGED, ALONG WITH ANODES, IN THE MAIN CHAMBER, AND WHEREIN MOLTEN MAGNESIUM IS RECEIVED ABOVE THE CATHODES WITHIN THE MAIN CHAMBER AND GUIDED THROUGH THE PARTTION WALL BENEATH THE SURFACE OF THE FUSED BATH INTO THE SUPPLEMENTAL CHAMBER FOR COLLECTION THERE, THE IMPROVEMENT WHICH COMPRISES THE STEPS OF MAINTAINING THE FUSED BATH AT A TEMPERATURE ABOVE THE MELTING POINT OF MAGNESIUM AND BELOW 700*C., AND KEEPING THE COLLECTED MAGNESIUM MOLTEN IN THE SUPPLEMENTAL CHAMBER BY RECEIVING AND COLLECTING THE MOLTEN MAGNESIUM, WHICH IS DIRECTED THROUGH THE PARTITION WALL, IN AN UPWARDLY ENCLOSED REGION THAT EXTENDS ALONG SAID SUPPLEMENTAL CHAMBER WITHIN THE LATTER AND THAT IS MAINTAINED SUBMERGED BENEATH THE SURFACE OF THE FUSED BATH, AND WITHDRAWING MOLTEN MAGNESIUM AS PRODUCT, FROM A LOCALITY OF SAID ENCLOSED REGION. 